1. Field of the Invention
The present invention relates to a thin-film magnetic head having at least an induction-type electromagnetic transducer, and to a method of manufacturing the same.
2. Description of the Related Art
Recent years have seen significant improvements in the areal recording density of hard disk drives. In particular, areal recording densities of latest hard disk drives have reached 80 to 100 gigabytes per platter and are even exceeding that level. It is therefore required to improve the performance of thin-film magnetic heads.
Among the thin-film magnetic heads, widely used are composite thin-film magnetic heads made of a layered structure including a recording (write) head having an induction-type electromagnetic transducer for writing and a reproducing (read) head having a magnetoresistive element (that may be hereinafter called an MR element) for reading.
In general, the write head incorporates: a medium facing surface (an air bearing surface) that faces toward a recording medium; a bottom pole layer and a top pole layer that are magnetically coupled to each other and include magnetic pole portions opposed to each other and located in regions of the pole layers on a side of the medium facing surface; a recording gap layer provided between the magnetic pole portions of the top and bottom pole layers; and a thin-film coil at least part of which is disposed between the top and bottom pole layers and insulated from the top and bottom pole layers. In the typical write head, the bottom pole layer and the top pole layer are magnetically coupled to each other via a coupling portion which is located away from the medium facing surface.
Higher track densities on a recording medium are essential to enhancing the recording density among the performances of the write head. To achieve this, it is required to implement the write head of a narrow track structure in which the track width, that is, the width of the two magnetic pole portions opposed to each other with the recording gap layer disposed in between, the width being taken in the medium facing surface, is reduced down to microns or the order of submicron. Semiconductor process techniques are utilized to achieve the write head having such a structure.
As the track width is decreased, it becomes harder to generate a high-density magnetic flux between the two magnetic pole portions that are opposed to each other with the recording gap layer in between. It is therefore desirable that the pole portions be made of a magnetic material having a higher saturation flux density.
When the frequency of the write signal is raised to increase the recording density, it is required for the write head that the speed of change of flux be improved, that is, the flux rise time be reduced. It is also required that degradation in the writing characteristics such as the overwrite property and the non-linear transition shift in a high frequency band be minimized. To improve the writing characteristics in the high frequency band, it is preferable to reduce the magnetic path length. The magnetic path length is determined chiefly by the length of a portion of the bottom or top pole layer located between the coupling portion and the medium facing surface (referred to as a yoke length in the present application). A reduction in yoke length is therefore effective in reducing the magnetic path length. To reduce the yoke length, it is effective to reduce the pitch of the turns of the thin-film coil, or the pitch of a portion of the turns which lies between the coupling portion and the medium facing surface, in particular.
One of prior-art techniques for reducing the pitch of turns of the thin-film coil is to form a recess in the bottom pole layer and dispose the thin-film coil in the recess. (See the U.S. Pat. No. 6,043,959 and the U.S. Pat. No. 6,259,583B1.)
According to the method of manufacturing a thin-film magnetic head disclosed in the U.S. Pat. No. 6,043,959, the bottom pole layer, the top pole layer and the thin-film coil are formed through the following steps. First, the bottom pole layer patterned into a specific shape is formed. Next, a recording gap layer and a magnetic layer are formed on the bottom pole layer one by one. A portion of the magnetic layer is coupled to the bottom pole layer. Next, masks are formed in a region in which a pole portion of the top pole layer is to be formed and in a region in which a coupling portion is to be formed. The magnetic layer, the recording gap layer and the bottom pole layer are etched, using the masks. As a result, a pole portion layer to be the pole portion of the top pole layer and a coupling layer to be the coupling portion are made up of the magnetic layer that has been etched. Through the above-mentioned etching, a trim structure is formed, wherein the sidewalls of the pole portion of the top pole layer, the recording gap layer and a portion of the bottom pole layer are formed vertically in a self-aligned manner. Furthermore, a recess in which the thin-film coil is to be disposed is formed in the bottom pole layer. Next, an insulating film is formed over the entire surface. The thin-film coil is then formed on the insulating film in the recess. Next, a thick insulating layer is formed over the entire surface and the top surface of the insulating layer is flattened, so that the pole portion layer of the top pole layer and the coupling layer are exposed. A yoke portion layer of the top pole layer is then formed on the flattened surface so as to couple the pole portion layer to the coupling layer.
According to the method of manufacturing a thin-film magnetic head disclosed in the U.S. Pat. No. 6,259,583B1, the bottom pole layer, the top pole layer and the thin-film coil are formed through the following steps. First, the bottom pole layer patterned into a specific shape is formed. Next, a pole portion layer to be the pole portion of the bottom pole layer and a coupling layer to be a coupling portion are formed on the bottom pole layer. Next, an insulating film is formed over the entire surface. The thin-film coil is then formed by plating on the insulating film, so that part of the coil passes between the pole portion layer and the coupling layer. Next, a thick insulating layer is formed over the entire surface and the top surface of the insulating layer is flattened, so that the pole portion layer and the coupling layer are exposed. A recording gap layer is then formed on the flattened surface. A contact hole is made in a region of the recording gap layer located above the coupling layer. Next, the top pole layer is formed on the recording gap layer. The top pole layer is connected to the coupling layer through the contact hole.
Another known technique for reducing the pitch of turns of the thin-film coil is to place the turns of a second coil between the turns of a first coil. (See the U.S. Pat. No. 6,191,916B1.)
As described above, it is desirable to reduce the yoke length of the thin-film magnetic head for improving the writing characteristics in the high frequency band. To achieve this, it is effective to reduce the pitch of part of the turns of the thin-film coil located between the coupling portion and the medium facing surface. On the other hand, it is desirable to increase the number of turns of the coil so as to improve the writing characteristics of the magnetic head.
To increase the number of turns of the coil and to reduce the yoke length at the same time, it is inevitable to reduce the width of the part of the coil located between the coupling portion and the medium facing surface. However, a problem that the resistance of the coil increases thereby arises.
As the resistance of the thin-film coil increases, there arises a problem that the pole portions may protrude toward the recording medium due to the heat the thin-film coil generates so that the pole portions are likely to collide with the recording medium.
Therefore, in the conventional thin-film magnetic head, to avoid the problem that may result from an increase in the resistance of the thin-film coil, it has been unfeasible to considerably reduce the yoke length.
The thin-film coil is typically formed through frame plating. The frame used for frame plating has walls each of which is disposed between adjacent turns of the coil. It is necessary that each of the walls be wide enough to maintain the shape of each of the walls. As a result, it is difficult to reduce the space between adjacent turns of the coil when the coil is formed through frame plating.
Through the use of the technique disclosed in the U.S. Pat. No. 6,191,916B1, it is possible to reduce the space between adjacent turns. In the thin-film magnetic head disclosed in the U.S. Pat. No. 6,191,916B1, however, the top pole layer including the pole portion that defines the track width is formed on an insulating layer covering the thin-film coil and rising like a plateau. It is therefore difficult to make the pole portion that defines the track width be small in size with precision.